In a packaging center where products intended for sale in supermarkets are packaged, a weighing and labelling system is generally employed for automatically and continuously executing jobs of weighing the products, calculating the price of each product based on the weight determined as a result of the product weighing job, printing the price and the weight on a respective label and applying the respective label to the corresponding product.
This weighing and labelling system is provided with a label printer for printing and issuing the price on the label and a label applying device for receiving the label issued by the label printer and applying it onto the product automatically. An example of this label applying device is disclosed in, for example, Japanese Utility Model Laid-open Application No. Sho-61-83508.
The prior art label applying device includes a suction head for sucking and holding a label issued from a label discharge opening of the label printer, a lift mechanism for lowering and elevating the suction head, and a drive motor for driving the lift mechanism and is so designed that, by lowering the suction head by means of the drive of the motor, the label held by the suction head can be applied to a product positioned below the suction head.
According to known prior art label applying devices, the suction head is elevated when the suction head receives a predetermined reactive force from the product. Therefore, when it comes to applying the label to an easily deformable product such as tofu or fried potato pudding, as shown in FIG. 15, the product C tends to be strongly pressed by a cushioning member B fitted to the suction head A to such an extent that the product C may be crushed or a marking of a press may be left on the product C, resulting in a reduction in commercial value of the product C.
Accordingly, so far as fragile products are concerned such as discussed above, labels are conventionally applied to the products manually.
In production factories a device is known which is so designed that, after a label holder has been lowered a predetermined distance by means of a pneumatic cylinder, switching is effected to apply air pressure required to elevate the label holder by detecting approach of the label holder towards the work, and wherein the label holder is caused to contact the work by the downward motion of the label holder thereby to apply the label to the work (See Japanese Utility Model Publication No. Hei-3-31687). According to this prior art, since the label is applied to the work while the air pressure has been switched in a condition required to elevate the label holder, the possibility of the product being damaged is reduced.
However, if, in an attempt to further avoid possible damage to the product, a lowermost limit position to which the label holder is lowered by the effect of an inertia is defined at a position very close to an upper surface of the product, the label applying device will fail to properly apply the label to the product due to a variation in stroke of downward movement of the label holder.
The present invention has been devised with due regard to the above discussed conventionally experienced problems, and has for its essential object to provide a labelling method and an apparatus therefor which are effective to minimize any possible damage to the products and also to properly apply the labels to the respective products.
Also, according to the foregoing prior art, since the label holder is lowered by the action of pneumatic pressure, the speed of downward movement tends to be so unstable as to result in a variation in stroke of downward movement by the effect of inertia. Also, since the viscosity of oil in sliding parts of the penumatic cylinder changes with changes in the temperature of surrounding air or that of the label applying device, deceleration of the label holder tends to be so unstable as to result in variation in stroke of downward movement by the effect of inertia. Accordingly, it often occurs that the stroke exceeds a predetermined value thereby imparting damage to the product, or the stroke falls short of the predetermined value thereby to fail to properly apply the label to the product.
Accordingly, another object of the present invention to minimize the variation in stroke of downward movement during application of the label to the product thereby to accomplish the above described object.